Method and apparatus for measurements of a characteristic of an object using a sensed signal and an auxiliary variable signal applied to the object

Abstract

An apparatus for measuring a measurable characteristic of an object includes a sensor element which emits an analog sensor output signal, the sensor output signal corresponding to the measurable characteristic of the object, an analog/digital converter for converting analog signals from the sensor element into digital output signals, a processor receiving the digital output signals and supplying a control signal to the controllable auxiliary variable generator. The controllable auxiliary variable generator is controlled by the control signal emitted by the processor, and the auxiliary variable signal is interrupted for a selected time span after each measuring interval. The processor filters out components of the measurable signal emitted by the sensor element which are caused by the auxiliary variable signal, by analyzing the signal produced by the controllable auxiliary variable signal generator together with the output signals from the analog/digital converter to form a resultant function, so that the processor can determine an accurate value of the measurable characteristic of the object.

We claim: 
     
       1. Method of measuring a measurable characteristic of an object in which the measurable characteristic of the object has a value which is sensed by a sensor element which emits an analog sensor output signal to a processor, the sensor output signal corresponding to the measurable characteristic of the object, based on the applied auxiliary variable signal and the sensor output signal corresponding to the measurable characteristic, comprising the steps of: supplying an auxiliary variable signal to the object from a controllable auxiliary variable signal generator, in which said auxiliary variable signal has a controllable time characteristic, said controllable auxiliary variable generator being controlled by a control signal emitted by the processor, and said auxiliary variable signal is interrupted for a selected time span after each measuring interval;   sensing the measurable characteristic of the object using the sensor element;   supplying the signal emitted by said sensor element to said processor as a digitalized measurement signal via an analog/digital converter; and   filtering out, using said processor, components or said measurable signal emitted by said sensor element which are caused by said auxiliary variable signal by processing of said control signal emitted by said processor to control said controllable auxiliary variable signal generator together with said signal emitted by said sensor element to form a resultant function with the auxiliary variable signal and the function similar to a cross-correlation function being such that the effects of said auxiliary signal on said measurable characteristic of the object detected by said sensor element are eliminated;   determining, using said processor, an accurate value of said measurable characteristic of the object based on the applied auxiliary variable signal and said resultant function such that effects produced by a linear noise component in said measurable characteristic of the object signal on the resulting determined value of said measurable characteristic are eliminated and the influence of digitalization errors on the resulting determined values of said measurable characteristic are minimized.   
     
     
       2. Method according to claim 1, further comprising repeating each of the steps a plurality of times and averaging the resulting plurality of determined values. 
     
     
       3. Method according to claim 1, wherein said auxiliary variable signal is at least one of time discrete and amplitude discrete. 
     
     
       4. Method according to claim 1, wherein said auxiliary variable signal is composed of at least one of a sequence of rectangular pulses of different time duration and a sequence of rectangular pulses of different amplitude. 
     
     
       5. Method according to claim 1, wherein said auxiliary variable signal has a time characteristic corresponding to that of a digital, multi-stage pseudo-random signal. 
     
     
       6. Method according to claim 1, wherein said auxiliary variable signal has a time characteristic similar to that of a multi-stage, digital, pseudo-noise signal which is interrupted after each measuring interval for a predeterminable period of time. 
     
     
       7. Method according to claim 1, wherein said auxiliary variable signal has a time characteristic corresponding to that of a digital, multi-stage, ternary pseudo-random signal of maximum length and minimum duration. 
     
     
       8. Method according to claim 1, wherein said auxiliary variable signal has a time characteristic corresponding to that of a multi-frequency, digital multi-stage signal. 
     
     
       9. Method according to claim 1, wherein said auxiliary variable signal is generated from said controllable auxiliary variable signal generator by at least one of changing the polarity of a supply voltage and switching out of a supply voltage. 
     
     
       10. Method according to claim 1, wherein said amplitude of said auxiliary variable signal is obtained from a reference voltage of said analog/digital converter. 
     
     
       11. Method according to claim 1, wherein said measurable characteristic of the object includes capacitance, inductance, resistance, and impedance; said auxiliary variable signal is a current flowing through the object being measured and said measured characteristic is a voltage applied across the object being measured. 
     
     
       12. Method according to claim 1, wherein said measurable characteristic of the object includes, inductance, resistance, and impedance; said auxiliary variable signal is a voltage applied to the object being measured and said measured characteristic is a current flowing through the object being measured. 
     
     
       13. Method according to claim 1, wherein, in said step of supplying an auxiliary variable signal, using bridge circuits, and providing a supply voltage for said measuring bridge from said auxiliary variable signal generator; and wherein said measured characteristic of the object is represented by the voltage of said bridge. 
     
     
       14. Method according to claim 1, wherein the object having said measurable characteristic is a structural component which is part of an active, electronic circuit. 
     
     
       15. Method according to claim 1, further comprising analyzing said resultant function and said auxiliary variable signal to determine at least one of cross-talk, electromagnetic couplings, and electromagnetic compatibility, with said auxiliary variable signal being utilized to control a noise source, and said signal from said sensor which represents said measurable characteristic of the object corresponding to an interfered-with circuit, and wherein said signal sensed by said sensor element from said interfered-with circuit has a pseudo-random characteristic. 
     
     
       16. Method according to claim 1 wherein said measurable characteristic of the object includes electrical and non-electrical variables, including variables which are capacitive, inductive, resistive, magnetic, electrical, optical, mechanical, physical, chemical, lengths, densities, masses, forces, temperatures, angles, radiation, light, substance concentration, substance composition, sound waves, moisture, pressures, expansion, turbidities, absorption spectra, fill levels, flow rate measurements and variables derived therefrom. 
     
     
       17. Apparatus for measuring a measurable characteristic of an object, comprising: a sensor element which emits an analog sensor output signal, said sensor output signal corresponding to the measurable characteristic of the object;   an analog/digital converter for converting analog signals from said sensor element into digital output signals;   processor means receiving said digital output signals, and supplying a control signal to said controllable auxiliary variable signal generator, said controllable auxiliary variable signal generator being controlled by said control signal emitted by said processor, said auxiliary variable signal being interrupted for a selected time span after each measuring interval; said processor means filtering out components of said measurable signal emitted by said sensor element which are caused by said auxiliary variable signal by analyzing said signal produced by said controllable auxiliary variable signal generator together with said output signals from said analog/digital converter to form a resultant function; whereby said processor determines an accurate value of said measurable characteristic of the object based on the applied auxiliary variable signal and said resultant function such that effects produced by a linear noise component in said measurable characteristic of the object signal on the resulting determined values of said measurable characteristic are eliminated and the influences of digitalization errors on the resulting determined value of said measurable characteristic are minimized;   wherein said processor is a microprocessor whose output is connected with a display unit and with said auxiliary variable signal generator so as to feed control signals to said auxiliary variable signal generator; wherein said output of said auxiliary variable signal generator feeds said auxiliary variable signal to the object being measured which is connected with said sensor element for picking up said measured value.   
     
     
       18. Apparatus according to claim 17, wherein said measurable characteristic of the object is capacitance, and wherein said auxiliary variable signal generator includes three switches of which said first switch is connected to a positive reference voltage, said second switch is connected to a reference potential and said third switch is connected to a negative reference voltage, with said positive and negative reference voltages being furnished by said analog/digital converter; the interconnected outputs of said switches are connected via a resistor with said inverting input of an operational amplifier whose non-inverting input is connected to said reference potential and whose output is connected, via said capacitance which is to be determined, with its inverting input and said output of said operational amplifier is connected with an input of said analog/digital converter, with said switches being actuated by said control signals emitted by said microprocessor.   
     
     
       19. Apparatus according to claim 17, wherein said auxiliary variable signal generator includes three switches of which said first switch is connected to a positive reference voltage, said second switch is connected to a ground or reference potential and said third switch is connected to a negative reference voltage, with said positive and negative reference voltages being furnished by said analog/digital converter; the interconnected outputs of said switches are connected via an inductance to be measured with said inverting input of an amplifier whose non-inverting input is connected to ground or a reference potential and whose output is connected, via a resistor, with its inverting input and said output of said operational amplifier is connected with an input of said analog/digital converter, with said switches being actuated by means of said control signal emitted by said microprocessor.   
     
     
       20. Apparatus according to claim 18, further comprising the step of changing measuring range of signals measurable by said auxiliary variable signal generator for measuring the capacitance of the object using further resistors connected in parallel with said resistors, and switching with the aid of said analog switches with a very low forward voltage, wherein said analog switches are composed of an operational amplifier including an analog switch in a feedback connection; wherein, in a switched-on state, said input signal is applied to said non-inverting input of said operational amplifier and said analog switch in a feedback line of said operational amplifier is closed so that said input signal produces said output signal at said inverting input; in a switched-off state, said non-inverting input is connected to a reference potential, via a second analog switch, with said analog switch being open so that said output signal of said analog switch at said inverting input of said operational amplifier is independent of said input signal. 
     
     
       21. Apparatus according to claim 17, wherein said auxiliary variable signal generator includes three switches of which said first switch is connected to a positive reference voltage, said second switch is connected to a ground or reference potential and said third switch is connected to a negative reference voltage, with said positive and negative reference voltages being furnished by said analog/digital converter; said interconnected outputs of said switches are connected to a measuring bridge as a supply voltage; wherein said bridge voltage is connected, via said sensor element with an input of said analog/digital converter; said switches being actuated by means of control signals emitted by said microprocessor. 
     
     
       22. Apparatus according to claim 17 used as a digital substitute for analog carrier frequency measuring bridges and measuring amplifiers. 
     
     
       23. Apparatus according to claim 17, wherein, for the electrical measurement of non-electrical variables, at least one of said auxiliary variable signal and said measured variable signal are non-electrical variables.